The present invention relates to a delivery apparatus for conveying printed sheets, and, delivering and stacking the sheets on a stack board in a sheet-fed printing press.
FIG. 8 is a side view showing a main part of a conventional delivery apparatus. Referring to FIG. 8, a pair of right and left delivery chains 5 are looped between a sprocket 2 arranged coaxially with a delivery cylinder opposing a printing cylinder and a sprocket 4 at the front end of a delivery frame 3. A plurality of pairs of gripper shafts are supported by the delivery chains 5 with predetermined intervals therebetween, and a plurality of pairs of gripper devices 6 (to be referred to as grippers 6 hereinafter) are formed on each gripper shaft. Printed sheets 7 are transferred from grippers of the printing cylinder to the grippers 6 of the delivery chains 5 by the delivery cylinder 1 cooperating with the printing cylinder and are conveyed by movement of the delivery chains 5. A stack board 8 is suspended by lifting chains 9 at its four corners below the terminal end of a sheet convey path. The sheets 7 released from the grippers 6 are dropped and stacked on the stack board 8. Reference numeral 10 denotes a jogger for abutting against and aligning the leading edges of the dropped sheets 7. At the terminal end of the conveying path of the sheets 7, a pair of right and left screw shafts 11 are axially supported by the delivery frame 3. A plurality of suction wheels 12 aligned in a sheet widthwise direction are provided to the screw shafts 11 through a suction wheel shaft or the like. Each sheet 7 is chucked at its trailing edge on the circumferential surfaces of the suction wheels 12 and decelerated. Therefore, the sheets 7 kept at high tension can be aligned well when they are dropped. If a sheet size is changed, the screw shafts 11 are rotated to move forward/backward the suction wheels.
In the above delivery apparatus, if printed surfaces of the sheets 7 stacked on the stack board 8 are not satisfactorily dried, offset occurs to degrade the quality of printed products. Therefore, a powder sprayer is conventionally located in the convey path and powders the printed surface of each conveyed sheet to prevent offset. That is, a nozzle pipe 13 having a large number of nozzle holes and extending in the sheet widthwise direction is located in inclined portions of the delivery chains 5 and connected to an air supply source through a solenoid and a powder container (neither of which is shown). As shown in an enlarged side view of FIG. 9, a cam 16 consisting of a stationary cam 14 and a movable cam 15 which can be phase-adjusted in a circumferential direction with respect to the stationary cam 14 is mounted on the shaft of the sprocket 4. A contact member 19 of a limit switch 18 electrically connected to the solenoid and supported by a bracket 17 is in contact with the cam surface of the cam 16. With this arrangement, when the cam 16 rotates together with the sprocket 4, the solenoid is opened/closed at a predetermined timing through the limit switch 18 each time the contact member 19 passes through a large-diameter portion of the cam surface, and the printed surface is powdered while the sheet 7 is conveyed through a corresponding portion of the nozzle pipe 13. If the sheet size is changed, the movable cam 15 is pivoted to increase/decrease a circumferential angle of the large-diameter portion, thereby prolonging/shortening a powdering time.
In the powder sprayer of the conventional delivery apparatus having the above arrangement, however, an operation corresponding to the sheet size is performed by phase adjustment of the cam 16. Therefore, no accurate adjustment can be expected, and it is troublesome to adjust the cam 16 each time the sheet size is changed because the sheet size is frequently changed. In addition, if the powdering time is too short, offset occurs to degrade the quality of printed products. For this reason, the powdering time is usually set longer in consideration of a safety margin. As a result, powder is wasted or scattered to contaminate the printing press or working environment.